Process of making tetra-alkyl lead



Patented Oct. 27, 1925.

1,559,405 PATENT OFFICE.

WILLIAM S. CALCOTT, OF PENNSGROVE, JERSEY, ASSIGNOR TO E. I DU PONT DE NEMOURS & COMPANY, OF WILMI INGTON,

DELAWARE.

.- No Drawing.

To all whom it may concern;

Be it known that I, WILLIAM S. CALCOTT,

a citizen of the United States, and a resident of Pennsgrove, in the county of Salem and State of New Jersey, have invented a certain new and useful Process of Making Tetra-Alkyl Lead, of which the following is a specification. 7

This invention relates to a process of pro- 10 ducing a tetra-alkyl lead, and comprises treating a lead-sodium alloy (for example, an alloy in which the ratio of lead to sodium is indicated by the formula PbNa with an alkyl halidein the presence of a catalyst of the type used for the Grignard synthesis, adding-water to the mixture thus formed, and maintaining the resulting lead compound for an apcpreciable time at a temperature above The alkyl derivatives with which this invention is.chiefly concerned are the combi nations of lead with alkyls having from one to four carbon atoms, namely with methyl, ethyl, nand iso-p'ropyl, and nand iso-butyl.

The alkyl halide used in the process is preferably an alkyl bromide or an alkyl iodide. y

The lead-sodium alloy used should pref,- erably be ground to increase the area of its surface.

Catalysts of the type used for the Grignard synthesis include such organic' compounds as contain a tertiary basic nitrogen atom (for example, dimethylaniline, triethylamine and pyridine), esters (such as ethyl acetate), ethers, etc. Any of these Grignard catalysts may be used to promote the reaction'between lead and alkyl halide, but I preferto use for this purpose the tertiary amines. I,

My invention .will be explained by de. scribing its application to the manufacture of tetra-ethyl lead (i. e., lead-tetraethide, Pb(C H this product being considered of most importance.

According to one proposed method of making tetra-ethyl lead, a lead-sodium alloy corresponding to the formula PbNa is mixed with pyridine and ehtyl bromide, and the mixture heated while slowly adding water equivalent to the sodium content of the lead alloy; The mechanism of this reaction, which yields tetra-ethyl lead, was not DELAWARE, A CORPORATION or gnocnss or MAKING TETRA-ALKYL LEAD.

Application filed October 5, 1922. Serial No. 592,598.

known. I have now discovered that it is unnecessary to have the lead alloyed with such an amount of sodium as to corresopnd V i to the formula PbNa any sodium in excess of an amount corres onding to .PbNa bemg not onlysuper uous, but also detrimental with respect to the progress of the reaction.

As is shown by these equations the essential feature of the reaction is the formation of the lead ethyl bromide complex, which upon reduction in the presence of ethyl bromide yields diethyl lead; this material being unstable above approximately 20 0;, breaks down with the formation of tetra ethyl lead and metallic lead.

The pyridine or other catalyst of the type used in the Grignard synthesis apparently serves to accelerate some combination or reactionbetween the lead and the alkyl bromide; The water used as the source of hydrogen may be so small in amount as to 'bealso regarded as a catalyst, for-it has been found that'the amount of water neces sary can be as little as 20% of that required to combine with the sodium present, as the water is continuously regenerated during the progress of the reduction by a secondary reaction between the sodium hydroxide and the hydrobromic or hydriodic acid formed. This was not true when using the tetra sodlum lead alloy, as in that case sufiicient water must be added to desti'oy the excess sodium present. r y new procedure may be illustrated by the following example I One hundred and sixty parts of coarsely -(10 mesh) ground alloy containing about 29 parts of sodium and 131 parts of lead are mixed at room'temperaturefwith 135 parts of ethyl bromide and 19.2 parts (all parts by weight) of triethylamine. The mixture is then placed in a bath whose temperature can be controlled. 4 parts of water are then added slowly to the mixture with con stant stirring, the rate of addition being controlled so that this amount of water is added in 16 hours, the temperature being 'held below 35 C. The reaction takes place smoothly, with evolution of heat. When the reaction is complete, as shown by the absence of alloyjifi a test portion, a large ex cessof water (200 cc.) is added, and the lead tetra-ethyl is steam distilled off.

The optimum temperature for the reaction appears to be 30 C., although temperatures as low as 5 C. and as high as 35 C. have been employed successfull Although in the preferred em iment of my invention the reduction of t e leadalkyl-halide mixture is brought about by the nascent hydrogen resulting from the action of an alkali-metal on water, my invention maybe said, generically, to comprise effecting the reduction of the lead-alkyl halide mixture by bringing into contact therewith preferably an amount of a reducing agent equivalent to not more than one-half of the lead used, but which in any case is substantially less than the equivalent of four atoms of nascent hydrogen for each molecule of the lead present in the reaction mix- =ture. The nascent hydrogen for this reduc tion may be furnished in various ways other than by the action of an alkali-metal on Water, this latter method, however, being preferred. As indicated by the specific example given above, it is not necessary to convert the lead into a lead-alkyl halide combination or complex before starting the reduction of the latter; in fact a considerable sav ing in time is effected by allowing these two reactions to proceed concurrently.

' Where the product desired is lead tetramethyl (Pb (CH lead tetra-propyl Pb C H,),), or lead tetra-butyl PbiC,H,) the directions of the specific example (supra) may be followed except that instead of ethyl bromide a stoichiometrically equivalent quantity of methyl, propyl, or butyl, bromide, as the case may be, is used.

I claim:

1. The process of producing a tetra-alkyl lead which comprises treating lead with an alkyl halide in the presence of a catalyst of the type used for the Grignard synthesis, and subjecting the mixture to the action of a suflicient quantity of a reducing agent to effect reduction to a lead dialkyl, and converting the latter by heat into tetra-alkyl lead, the quantity of said reducing agent being substantially less than the equivalent of four atoms of nascent hydrogen, for each molecule of the lead used.

2. The process of producing a tetra-alkyl lead which comprises treating lead with an alkyl halide under conditions controlled to produce a lead-alkyl halide combination, subjecting the resulting mixture to the action of a suflicient quantity of a reducing agent to produce a lead dialkyl, and con"- verting the latter by heat into tetra-alkyl lead, the quantity of said reducing agent being substantially less than the equivalent of four atoms of nascent hydrogen, for each molecule of the lead used.

3. A process of the kind set forth in claim 1 in which the catalyst is a tertiary amine.

4. A process of the kind set forth in claim 1 in which the reducing agent is hydrogen generated in situ by the action of an alkalimetal on water.

5. The process of producing tetra-ethyl lead which comprises treating lead with an ethyl halide in the presence of a catalyst of the type used for the Grignard synthesis, subjecting the resulting mixture to the action of a-sufiicient quantity of a reducing agent to produce di-ethyl lead, and converting the latter by heat into tetra-ethyl lead, the quantity of said reducing agent being substantially less than the equivalent of four atoms of nascent hydrogen, for each molecule of the lead used.

6. The process of producing tetra-ethyl lead which comprises treating lead with an ethyl halide under conditions controlled to produce a lead-ethyl halide combination, subjecting the resulting mixture to the action of a sufficient quantity of a reducing agent to effect reduction to (ii-ethyl lead, and converting the latter by heat into tetra-ethyl lead, the quantity of, said reducing agent being substantially less than the equivalent of four atoms of nascent hydrogen, for each molecule of the lead used.

7. A rocess of the kind set forth in claim 5 in which the catalyst is a tertiary amine.

8. A process of the kind set forth in claim 5 in which the reducing agent is hydrogen generated in situ by the action of an alkalimetal on water.

9. A process of the kind set forth in claim 1 in which the catalyst is dimethylaniline.

10. A process of the kind set forth in claim 5 in which the catalyst is dimethylaniline.

11. The process of producing tetra-ethyl lead which comprises treating a lead-sodium alloy in which the proportion of sodium is at least two atoms, and less than four atoms, for each atom of lead, with ethyl bromide and a catalyst of the type used for the Grignard synthesis, gradually adding water to the reaction mass until the lead-ethyl bromide mixture is converted to di-ethyl lead, and causing the temperature of the mixture to rise above 20 C. for a suflicient time to effect the conversion of di-ethyl lead to tetra-ethyl lead.

12. A process of the kind set forth in claim 11 in which the catalyst is an organic compound containing a tertiary basic nitroen atom.

13. The process of producing tetra-ethyl 0., then adding a large excess of water, and heating the resulting mixture sufiiciently to distill off tetra-ethyl lead.

14. In the process of producing a tetraalkyl lead, the step which comprises mixing an alloy having the composition PbNa With an alkyl halide and a catalyst of the type used for the Grignardsynthesis, to form a lead-alkyl halide mixture intimately associated with sodium.

15. In the process of producing tetraethyl lead, the step which comprises mixing coarsely ground PbNa with ethyl bromide and a tertiary amine to form a lead-ethyl bromide mixture intimately associatedwith sodium.

16. In the process of producing tetra- 18. In the process of producing tetraethyl lead, the step which comprises subjecting to the action of a reducing agent a lead-ethyl halide mixture obtainable by treating lead with an ethyl halide in the presence of a catalyst of the type used to the Grignard synthesis, the quantity of sai j; reducing agent being substantially less than '35 the equivalent of four atoms of nascent hydrogen, for each molecule of the lead used.

19. In the process of producing tetraethyl lead, the stepwhich comprises sub- 40 jecting to the action of areducing agent a lead-ethyl bromide mixture obtainable byv treating lead with ethyl bromide in the presence of a catalyst of the type used for the Grignard synthesis, the quantity of said reducing agent being substantially less than the equivalent of four atoms of nascent hydrogen, for each molecule of the lead used.

20. A process of the kind set forth in claim 11 in which the catalyst is dimethylaniline.

In testimony whereof I afiix my signature.

' WILLIAM S. OALCOTT. 

